1. Field of the Invention
This invention relates to an extrusion die, having a first die element and a second die element, each of which has a die lip, between which an extrusion gap with a slot-shaped outlet opening extends over the width of the extrusion die, wherein at least one die element has an adjusting device by which the die lip can be adjusted in relation to the die lip of the other die element while changing a width of the outlet opening. The adjusting device has an adjusting bar arranged in a receiving groove of the die element and displaceable in the width extension thereof in a displacement device, which bar has at least one sliding cam laterally projecting past the adjusting bar. Each sliding cam is guided in a control groove of the die element, wherein the control groove is arranged to run obliquely with respect to the displacement direction of the adjusting bar, so that when the adjusting bar is displaced in the displacement direction, with the engagement of the at least one sliding cam in the control groove it is possible to achieve a displacement of the die lip extending transversely to it.
2. Description of Related Art
Because of the slot-shaped outlet opening extending across the width of the extrusion die, such extrusion dies are often called slot dies and are used for the extrusion of flat foils, flat sheets and flat panels, as well as for extrusion coating.
While the width of the foil, sheet, panel or coating on the basis of thermoplastic material extruded by the extrusion die is fixed by a width of the outlet opening, there are adjusting devices that vary the width of the outlet opening, for example the dimension perpendicularly to the width of the extrusion die, for changing the thickness of the plastic strand coming out of the extrusion die.
An adjusting device of the species with an adjusting bar, which is seated, displaceable in the width of the extrusion die, and with projecting sliding cams engage control grooves of the die element in order to cause an adjustment of the width of the outlet opening, is known from German Patent Reference DE 94 22 051 U1 and European Patent Reference EP 0668 143 B1. This is a so-called flex-lip, wherein the die lip to be adjusted is fastened flexibly and bendable on the die element and is bent more or less in the direction of the other die lip by the adjusting device for setting the outlet opening. In this known embodiment the adjusting bar is guided, directly adjustable, in an appropriate receiving groove of the die element, and the protruding or projecting sliding cams are directly guided in appropriate control grooves. However, in actual use large frictional forces are generated by this direct guidance of the adjusting bar and the sliding cams in the respective receiving groove or the control grooves which, to assure correct functioning, requires even and adequate lubrication of the faces sliding off on each other. This requires considerable maintenance and cannot always be maintained over an extended use time and can lead to increased wear of the adjusting device. In actual use this results because in the course of extensive usage of the known adjusting device and/or large dimensions of the extrusion die the actuating forces for causing the desired adjusting movement increase beyond sensible and manageable threshold values.
It is one object of this invention to provide an extrusion die with an adjusting device of the type mentioned above but so that it is possible, even with continuous operation and/or with large extrusion die dimensions, to achieve a smooth-running and dependable adjustment of the die lips, along with reduced maintenance outlay, wherein an easy adjustment during operation is particularly possible.
This object is achieved with further development of an extrusion die as discussed in the claims and this specification.
In accordance with this invention, the adjusting bar and/or at least one sliding cam of the adjustment bar are arranged, respectively with the interposition of a roller chain, in the receiving groove or control groove.
The direct sliding off of the adjusting bar or its projecting sliding cam in the receiving groove or the control groove of the die element is thus prevented and the desired mobility is provided by the roller chains. The roller chains, preferably arranged between the adjusting bar and the receiving groove, as well as between the sliding cam and the control grooves, provide a smooth-running displaceability of the adjusting bar and a resultant smooth-running adjustment of the width of the outlet opening of the extrusion die, even with a large size of the extrusion die and/or over large adjustment distances.
The adjusting device of this invention, having roller chains arranged between the adjustment bar and the receiving groove and/or between the projecting sliding cam and the control groove, can be used in connection with various known designs of so-called slot extrusion dies.
In one embodiment of the extrusion die of this invention, a so-called adjusting lip, wherein the die element having the adjusting device is embodied in several parts and with a rear die element and a front die element, which is attached to the front of the latter and contains the die lip, and is displaceable with respect to the rear die element by the adjusting device while changing the width of the outlet opening of the extrusion gap. In contrast to adjustment by flexibly attached tool lips, an adjustment of the extrusion gap by a displaceable tool lip has one advantage that the flow surfaces of the extrusion gap providing the shaping remain parallel with each other over the entire adjustment range. Large adjustment ranges, and therefore large adjustable areas for the width of the outlet opening of the extrusion gap, can be set by an extrusion die having an adjusting lip, wherein the adjusting forces are reduced by the roller chains in accordance with this invention.
It is possible during continuous operation to adjust the extrusion die of this invention on demand.
In this case the receiving groove for receiving the adjusting bar is preferably formed in the rear die element and is open toward the front die element. The control grooves for receiving the sliding cams of the adjusting bar are formed in the front die element on the side resting against the rear die element. However, this embodiment is not mandatory and can be changed. For example, the adjusting bar can be housed in a receiving groove in the front die element while the control grooves receiving the projecting sliding grooves are housed in the rear die element. It is also possible for the adjusting bar to have control cams in lieu of projecting sliding cams, which are engaged by correspondingly embodied projecting sliding cams at the front die element or rear die element.
In another embodiment of the extrusion die in accordance with this invention, in the so-called flex-lip style, wherein the die element with the adjusting device has a die lip arranged on it in a flexible and bendable manner, and wherein bending of the die lip by the adjusting device and an accompanying change in the size of the outlet opening of the extrusion die can be achieved. Such flex-lip extrusion dies are known in many forms, and reference is made merely by way of example to German Patent Reference DE 94 22 051 U1 and European Patent Reference EP 0 668 143 B1.
The structure of the roller chains arranged between the adjusting bar and the receiving groove and/or between the sliding cam and the control groove is important for the function of the extrusion die of this invention.
The roller chains are preferably designed endlessly revolving, so that their friction-reducing and function-enhancing properties are available over an entire adjustment range of the extrusion die of this invention.
In one embodiment of the roller chains of this invention, a plurality of respective rollers are rotatably seated in the lateral members, on which the adjusting bar in the receiving groove, or the at least one sliding cam in the associated control groove, roll off in relation to each other. The rollers rotatably seated in the lateral members are chained together at their respective ends with lateral members in a known manner.
To assure a sufficient stability of the roller chains of the extrusion die of this invention, there are connecting bridges which connect the respective lateral members of the roller chain with each other, in areas between adjoining rollers.
In order to be able to permanently absorb the expected high displacement forces, the roller chains are preferably manufactured from suitable hardened steel or other material suitable for the load.
With the extrusion die in accordance with this invention, it is possible to adjust the width of the outlet opening up to 12 mm.
It is also possible within the scope of this invention to use different chain forms.